An IP multimedia subsystem (IMS) is a telecommunications network subsystem providing IP multimedia services that complement the services provided by mobile networks. The IMS enables the support for IP multimedia applications within the third generation mobile systems by enabling mobile network operators to offer multimedia services based on Internet applications, services and protocols. These protocols include a Session initiation protocol SIP, which is used to manage the IP multimedia sessions. Users of the IMS technology may utilize applications like presence services, interactive applications, content sharing and real-time video. Also push-to-talk connections are based on the IMS technology. Any network supporting the IP protocol may be utilized in the IMS technology. Examples of such networks include GPRS (General packet radio service), WCDMA (Wideband code division multiple access), WLAN (Wireless local area network) and B-ISDN (Broadband integrated services digital network) networks.
The IMS technology also enables a solution where a local IP multimedia resource, such as a multimedia PC (personal computer) connected to the Internet, is reserved and controlled by means of a user terminal, such as a mobile station connected to the IMS network.